MN short or long on front on its own stops a small amount of mud. My face will still be covered in muck, and so would my eyes (which is what i want to stop).
Recently got the gut fender to go with. Eyes are now about 90% mud free. Much better, and only £4.50:-)

Thought I may a well add to this thread. Bought a rear MN rear full fender and it lasted all but a week. Lightly caught my leg on it a couple of times and it has snapped where the strap mounts it to the seat post. Definitely stopped a lot of spray on my back but they really are not robust at all, so would recommend looking for an alternative despite the cheap price.

Yeah, the design is flawed. Mine broke in the same place. There are just four narrow strips holding the thing together at that point. I quite liked it as a low weight, reasonably effective option, but it's fragile as... Meanwhile the Mudhugger on my winter hack bike is hideous, but incredibly effective. I'd avoid the MN rear fender until they redesign the thing.

Badly WD - yes exactly where mine has broken. It needs a re-design for sure. I have mailed them about it as i think they need to know. They are a great company but the rear fender does not cut it. I don't normally do mud guards but this year I thought why exactly am I riding around getting covered in the black stuff uneccessarily. Bender fender has worked a treat up front. It's been great having a dry back for a few rides so I definitely want another rear guard of some sort despite how ugly they look. Will take a look at the mud hugger.

I've broken 3 of these things.
utterly useless.
i've even "tested" their uprated version which they are due to release soon.
still shite!

I have a mudhugger now.
Granted it's not the most sexy looking peice of kit but i don't care and i don't look like i've had managed to crap up my back and beyond.
He is a local guy to me and was really nice when we met him.

I'm part way through modding the broken MN Rear Fender to sit on the butchered mount from an old Crud Catcher rear. Plan is to fit it below the seatpost QR on my hardtail so I can still drop the seatpost.

I'm not sure it's an elegant solution, but it looks like it should work. I think and be considerably more robust than the original fitting.

For what it's worth, I've had the rear seatpost mounted one and other than having to do it up really tight to stop it spinning it's been about what I expected- not as good as a proper guard but significantly better than nothing. I prefer a proper guard, but the mn one fits a lot better with the reverb. Not long enough to be useful on a 29 though.

I was fairly impressed it survived acting as the intermediary in an arse/tyre interface completely unscathed though. I did have a couple of thoughts about improving the clamp area, whether they ever get done is a different question.